"""
Acceleration and Friction

Demonstrate how to implement simple acceleration and friction without a
physics engine.

Artwork from https://kenney.nl

If Python and Arcade are installed, this example can be run from the
command line with:
python -m arcade.examples.sprite_move_keyboard_accel

加速及摩擦

演示如何在没有物理引擎的情况下实现简单的加速和摩擦

底层逻辑是：
按键控制加速度->加速度控制速度->速度控制位置

"""

import arcade

# 精灵大小
SPRITE_SCALING = 0.5

# 窗口大小和标题
WINDOW_WIDTH = 1280
WINDOW_HEIGHT = 720
WINDOW_TITLE = "Better Move Sprite with Keyboard Example"

# Important constants for this example

# Speed limit
# 最大速度
MAX_SPEED = 3.0

# How fast we accelerate
# 加速大小
ACCELERATION_RATE = 0.1

# How fast to slow down after we let off the key
# 摩擦大小。注：摩擦大小必定小于加速大小
FRICTION = 0.02


class Player(arcade.Sprite):

    def update(self, delta_time: float = 1/60):
        # 根据变更速度移动
        self.center_x += self.change_x
        self.center_y += self.change_y

        # self.left,self.right,self.top,self.bottom继承自arcade.Sprite，表示上下左右的边界坐标（省了计算边界的工夫）
        # self.change_x和self.change_y可以理解为横轴和纵轴的速度
        # Check to see if we hit the screen edge
        if self.left < 0:
            # 如果和左侧碰撞，则精灵左侧和左边界对齐，并重置横轴速度
            self.left = 0
            self.change_x = 0  # Zero x speed
        elif self.right > WINDOW_WIDTH - 1:
            # 如果和右侧碰撞，则精灵右侧和右侧边界对齐，并重置横轴速度
            self.right = WINDOW_WIDTH - 1
            self.change_x = 0

        if self.bottom < 0:
            #  如果和底部碰撞，则精灵底部和底部边界对齐，并重置纵轴速度
            self.bottom = 0
            self.change_y = 0
        elif self.top > WINDOW_HEIGHT - 1:
            #  如果和顶部碰撞，则精灵顶部和顶部边界对齐，并重置纵轴速度
            self.top = WINDOW_HEIGHT - 1
            self.change_y = 0


class GameView(arcade.View):
    """
    Main application class.
    """

    def __init__(self):
        """
        Initializer
        """

        # Call the parent class initializer
        super().__init__()

        # Variable to will hold the player sprite list
        # 声明精灵列表
        self.player_list = None

        # Create a place to store the player sprite
        # so it can be  accessed directly.
        # 声明玩家精灵
        self.player_sprite = None

        # Create places to store the speed display Text objects
        # 声明横轴速度展示
        self.x_speed_display = None
        # 声明纵轴速度展示
        self.y_speed_display = None

        # Track the current state of what key is pressed
        # 声明上下左右4个按键是否按下
        self.left_pressed = False
        self.right_pressed = False
        self.up_pressed = False
        self.down_pressed = False

        # Set the background color
        # 初始化背景颜色
        self.background_color = arcade.color.AMAZON

    def setup(self):
        """ Set up the game and initialize the variables. """

        # Create a sprite list
        # 初始化玩家精灵列表
        self.player_list = arcade.SpriteList()

        # Set up the player
        # 初始化玩家精灵（图像，scale，位置），并装载到精灵列表
        self.player_sprite = Player(
            ":resources:images/animated_characters/female_person/femalePerson_idle.png",
            scale=SPRITE_SCALING,
        )
        self.player_sprite.position = self.width / 2, self.height / 2
        self.player_list.append(self.player_sprite)

        # Create the speed display objects with initial text
        # 初始化横轴速度展示
        self.x_speed_display = arcade.Text(
            f"X Speed: {self.player_sprite.change_x:6.3f}",
            10, 50, arcade.color.BLACK, font_size=15,
        )
        # 初始化纵轴速度展示
        self.y_speed_display = arcade.Text(
            f"Y Speed: {self.player_sprite.change_y:6.3f}",
            10, 70, color=arcade.color.BLACK, font_size=15,
        )

    def on_draw(self):
        """
        Render the screen.
        """

        # This command has to happen before we start drawing
        # 通用指令
        self.clear()

        # Draw all the sprites.
        # 精灵列表绘画
        self.player_list.draw()

        # Draw the speed indicators
        # 横纵轴速度展示绘画
        self.x_speed_display.draw()
        self.y_speed_display.draw()

    def on_update(self, delta_time):
        """ Movement and game logic """

        # Add some friction
        # 如果横轴正向速度大于摩擦力，则持续通过摩擦力减少；反之亦然
        if self.player_sprite.change_x > FRICTION:
            self.player_sprite.change_x -= FRICTION
        elif self.player_sprite.change_x < -FRICTION:
            self.player_sprite.change_x += FRICTION
        else:
            # 如果在摩擦力区间内，则速度直接置零
            self.player_sprite.change_x = 0

        # 纵轴速度与横轴速度逻辑一致
        if self.player_sprite.change_y > FRICTION:
            self.player_sprite.change_y -= FRICTION
        elif self.player_sprite.change_y < -FRICTION:
            self.player_sprite.change_y += FRICTION
        else:
            self.player_sprite.change_y = 0

        # Apply acceleration based on the keys pressed
        if self.up_pressed and not self.down_pressed:
            # 如果按了上键且未按下键，则给纵轴一个正向的加速度
            self.player_sprite.change_y += ACCELERATION_RATE
        elif self.down_pressed and not self.up_pressed:
            # 如果按了下键且未按上键，则给纵轴一个负向的加速度
            self.player_sprite.change_y += -ACCELERATION_RATE
        if self.left_pressed and not self.right_pressed:
            #  如果按了左键且未按右键，则给横轴一个负向的加速度
            self.player_sprite.change_x += -ACCELERATION_RATE
        elif self.right_pressed and not self.left_pressed:
            #  如果按了右键且未按左键，则给横轴一个正向的加速度
            self.player_sprite.change_x += ACCELERATION_RATE

        # 如果玩家精灵在任意方向超过了最大速度，则保持在最大速度
        if self.player_sprite.change_x > MAX_SPEED:
            self.player_sprite.change_x = MAX_SPEED
        elif self.player_sprite.change_x < -MAX_SPEED:
            self.player_sprite.change_x = -MAX_SPEED
        if self.player_sprite.change_y > MAX_SPEED:
            self.player_sprite.change_y = MAX_SPEED
        elif self.player_sprite.change_y < -MAX_SPEED:
            self.player_sprite.change_y = -MAX_SPEED

        # Call update to move the sprite
        # IMPORTANT: If using a physics engine, you need to call update
        # on it instead of the sprite list!
        # 更新玩家精灵列表
        self.player_list.update(delta_time)

        # Update the speed displays based on the final speed
        # 更新展示速度，格式为6.3f
        self.x_speed_display.text = f"X Speed: {self.player_sprite.change_x:6.3f}"
        self.y_speed_display.text = f"Y Speed: {self.player_sprite.change_y:6.3f}"

    def on_key_press(self, key, modifiers):
        """Called whenever a key is pressed. """

        if key == arcade.key.UP:
            self.up_pressed = True
        elif key == arcade.key.DOWN:
            self.down_pressed = True
        elif key == arcade.key.LEFT:
            self.left_pressed = True
        elif key == arcade.key.RIGHT:
            self.right_pressed = True

    def on_key_release(self, key, modifiers):
        """Called when the user releases a key. """

        if key == arcade.key.UP:
            self.up_pressed = False
        elif key == arcade.key.DOWN:
            self.down_pressed = False
        elif key == arcade.key.LEFT:
            self.left_pressed = False
        elif key == arcade.key.RIGHT:
            self.right_pressed = False


def main():
    """ Main function """
    # Create a window class. This is what actually shows up on screen
    window = arcade.Window(WINDOW_WIDTH, WINDOW_HEIGHT, WINDOW_TITLE)

    # Create and setup the GameView
    game = GameView()
    game.setup()

    # Show GameView on screen
    window.show_view(game)

    # Start the arcade game loop
    arcade.run()


if __name__ == "__main__":
    main()